Wet chemical precipitation synthesis of hydroxyapatite (HA) powders

Abstract

Hydroxyapatite (HA) can be defined as a major member of bioceramic materials world. Production of HA in different forms, especially powder, is still worth to be investigated depending on the development of additive manufacturing systems which get attention in biomedical market, recently. Therefore, in this research, it is aimed to synthesize HA powders following the wet chemical precipitation technique and perform a detailed characterization including chemical, physical, microstructural and mechanical studies. Reaction temperature (30 °C, 50 °C and 85 °C), acid addition rate (slow and rapid acid addition rates) and heat-treatment temperature (950 °C and 1250 °C) were the considered process parameters. After the reaction between the alkaline (calcium hydroxide, Ca(OH)2) and acid (ortho-phosphoric acid, H3PO4) precursors, maturation of the precipitate, decantation of the precipitate and the by-product, drying and eventually heat-treating the precipitate were sequentially done. X-Ray Diffraction (XRD) analyses, Fourier Transform Infrared Spectroscopy (FT-IR) analyses, Differential Thermal-Thermogravimetric Analysis (DTA-TGA), Scanning Electron Microscope/Energy Dispersive Spectroscopy (SEM/EDS) observations, Vickers microhardness and compression strength tests and bulk density, apparent porosity (%) measurements based on the Archimedes’ Principle were carried out to characterize the synthesized HA powders and HA pellets. It is found that a low reaction temperature such as 30 °C and rapid acid addition rate (5.5 ml/min) are proper process parameters to acquire uniform and spherical-like HA powders with ~ 0.2–0.3 µm mean particle size. HA pellets exhibit a high amount of apparent porosity (~ 23–26%) and this situation can be indicated as an important advantage for the transition and penetration of the body fluids towards the pores.